I really hope that multiplayer doesn't forget us who don't play online, but rather over System Link. We do exist!
First of all, in the multiplayer maps, don't make them all for large parties. There needs to be at least a couple maps that are optimal for a smaller group, even just 4 people (that's the usual system link amount of players). And not just the symmetrical, round arena, but something interesting. And it doesn't have to be a tiny map, either. The Halo 3 map Standoff was a perfect example of an extremely entertaining map for just a few people, while still having a fairly large area. One of the biggest issues in Reach for our group was the fact that there was a lack of maps for our 4-player system link games. In Halo 3 (and all the Halos before) there was a ton of great maps, almost all of them suitable except for the massive ones. In Reach, just a couple were playable.
Now, I feel that while this is the most minor issue, it is also the most important:
In system link we often play custom game types, and one thing that we've played a lot over all the Halos is Random (with random weapons, infinite ammo, no weapon pickup (but that's not really the point, just background information)). Now, in that mode there are certain weapons that have basically decided the game alone. Especially the fuel rod gun in Reach was a game-breaker. What I'd hope for multiplayer game settings is that you can choose what weapons can appear on the map (or, in the case of our Random settings, for the player). Either a check-box type system, or at least a sort of "no heavy" "no snipers" "only human" etc. choices. A minor change, but a huge difference on the enjoyability of the game.
Of course, optimally, if there is this new game type I'm reading about, it would be also playable through system link. I guess it might be difficult if it has a reward system of some sort, though I'd still hope it would be workable if only even as a temporary offline system. It's fun change sometimes to play Firefight, and it'd be too bad if we wouldn't have that alternative choice anymore. But as long as the multiplayer were good, it wouldn't matter so much. So, I hope you take at least my second point into consideration.
(Edit: Oh, and since there's apparently going to be armor abilities again, why not the option of randomly chosen armor abilities too? (like random with each respawn))
Okay, thanks for listening